Magnetic amplifier circuit protecting devices



July 14, 1959 M. P. SIEDBAND 2,895,085

MAGNETIC AMPLIFIER CIRCUIT PROTECTING nsvxcas Filed D60. 20, 1956 00 65m w. w m 66 2 u T/ m s-l- W M 8 R 4 E 5 6 56 E R c R R R 0 O O 3 S S EMEA M IL L IL m WW mu E E R R R 88 9/ 9'91NVENTOR ME L V/IV I? S/EDBANO 7'4? j I ATTORNEYS 5 V. AC.

FIG. 2

MAGNETIC AlVlPLIFIER CIRCUIT PROTECTING DEVICES Melvin P. Siedband,Baltimore, Md., assignor, by mesne assignments, to the United States ofAmerica as represented by the Secretary of the Navy Application December20, 1956, Serial No. 629,764

2 Claims. (Cl. 317-31) The present invention relates to magneticamplifier circuit protecting devices and more particularly to magneticamplifier circuit protecting devices having overcurrent, undervoltageand/or overvoltage protection.

Circuit protection in apparatus such as radar power supplies consists ofplacing a fuse in series with each of the supplied voltages and a mainfuse. One disadvantage of this arrangement is that one of the fuses in abias supply circuit, for example, could blow out with plate voltagestill maintained: -this could cause serious damage to the vacuum tubes.Thus a device is needed to turn off the entire system in the event ofloss of bias.

The present invention embodies a magnetic amplifier which is notsensitive to environmental conditions such as temperature, for example,and which operates by the comparison of power supply voltages to a knownreliable voltage. The output of the magnetic amplifier operates a relayin response to oveivoltage, undervoltage and/ or excessive current flow,which opens the main supply circuit and thus prevents damage to thevacuum tubes.

An object of the present invention is the provision of a protectivesystem.

Another object of the invention is to provide an overvolta'ge,undervoltage, and/ or overcurrent protective systern.

A further object of the invention is the provision of an overvoltage,undervoltage, and/or overcurrent protective system for radar powersupplies.

Still another object of the invention is the provision of a protectivesystem which is not sensitive to environmental conditions.

Other objects and many of the attendant advantages of this inventionwill be readily appreciated as the same becomes better understood byreference to the following detailed description when considered inconnection with the accompanying drawings wherein:

Fig. 1 shows a schematic diagram of one embodiment of the invention.

Fig. 2 shows a schematic diagram of a second embodiment of the inventionapplied to a typical radar supply system.

Referring now to the drawings, wherein like reference charactersdesignate like or corresponding elements in each of the two figures,there is shown in Fig. 1 a selfsaturating magnetic amplifier 11 havingload winding 12, 13, and self saturating diodes 14 and 16. The output ofthe magnetic amplifier 11 is connected to a solenoid coil 27 of relay 17through a full wave rectifier 18 having input terminals 19 and 21 andoutput terminals 22 and 23. A smoothing capacitor 24 is connected acrossthe output terminals 22 and 23. The relay 17 is connected in series witha source, not shown, and has a contact 25 which is mechanicallyconnected to an armature 26 which is actuated by the solenoid coil 27. Asolenoid latch 28 is provided to latch the relay in an open position. Aremote control, not shown, is provided for resetting the magneticamplifier.

Each leg of the magnetic amplifier 11 has an overnited States Patentcurrent control winding 29, an undervoltage control winding 31, anovervoltage control winding 32 and a bias winding 33. The overcurrentcontrol winding 29 is connected in series with the circuit to beprotected having an input terminal 34 and an output terminal 35. Twodropping resistors, 36 and 37 are connected between the input terminal34 and ground. Control winding 31 is connected in series with a blockingrectifier 38 between the junction terminal 39 of the resistors 36 and 37and a terminal 41 of a reference voltage source, not shown, throughdropping resistors 42 and 43 and across a dropping resistor 44. The biaswinding 33 is connected to the reference voltage terminal 41 through afixed resistor 46 and a variable resistor 47.

In operation, by way of example, there is shown a +250 power supply forsuppling radar circuits. The voltage at the junction of resistors 36 and37 will be at +50 volts under normal conditions. If this voltage risesor falls ten percent, current will flow in either the overvoltagecontrol winding or the undervoltage control winding, thus causing themagnetic amplifier to saturate which allows a current to flow to operatethe relay 17 which will open the supply circuit. The overcurrent winding29 is connected in series with the +250 volt line, therefore a flux isestablished which is proportional to the current flowing in the circuit.Resistors 46 and 47 determine a bias current which produces a biasingflux to buck out the effect produced by the overcurrent Winding 29 aslong as the flux in the winding 29 remains well below the level of thebias flux. As the output current increases, a value will be reachedwhere the bias no longer holds the magnetic amplifier cut off and therelay 17 operates to open the supply circuit.

Fig. 2 shows a transformer 43 having a primary winding 49 and secondarywindings 51, 52 and 53. Primary winding 49 is connected to analterntaing current source, not shown, through the relay i7. Each of thesecondary windings 51, 52 and 53 is connected through bridge rectifiers55, 56 and 57 respectively to provide power for a plurality ofelectronic circuits, not shown. The output of rectifier 55 is fedthrough a filter circuit 59 and a series regulator to a supply lead 61of an electronic circuit, not shown. A series resistor 62 is connectedbetween the negative terminal of the rectifier 55 and ground. Rectifier56 is similarly connected to supply lead 64 through the filter network63. A further output voltage supply lead 65 is provided by a droppingresistor 66 and a series regulator. A resistor 67 is connected betweenthe negative terminal of rectifier 56 and ground.

The output of rectifier 57 is connected to provide negative voltagesupply circuits to leads 68 and 69. Supply leads 68 and 69 respectivelyare connected in series with resistor 58. Thus, the voltage drop acrossresistor 58 is proportional to the total current flowing in the twosupply leads 68 and 69. A voltage divider comprising three seriesconnected resistors 94, and 96 is connected between supply lead 68 andground. Terminal D is connected intermediate resistors 95 and 96 toprovide a negative voltage proportional to the negative supply voltageat 69. A shunt regulator is connected between supply line 69 and groundto maintain the voltage substantially constant. A filter circuit 71 isconnected across the output of rectifier 57.

The self-saturating magnetic amplifier 72 is of the two core type and issimilar to the amplifier 11 of Fig. 1 with the addition of a fifthwinding. Amplifier 72 is provided with an alternating current input 73,load windings 74, 75, and self-saturating rectifiers 76, 77. The output78 of the amplifier is connected to relay coil 27 through the rectifier18. Each core of the amplifier is provided with a bias winding 79,current control windings 81, 82, 83 and a voltage control winding 84.One

terminal of the bias winding 79 is connected through a variable resistor85 to the positive terminal 86 of a bias source, not shown, while theother terminal is connected to ground. Windings 82, 83, and 84 areconnected in series with blocking rectifiers 87, 88 and 89 respectivelyand a resistor '91 between the negative terminals B, A and Drespectively and the negative terminal 99 of the bias source. Winding 81is connected in series with a rectifier 92 and resistor 93 between thepositive terminal 86 of the bias source and the positive terminal C ofthe positive side of resistor 58. Resistors 97 and 98 are provided togive the proper biasing voltage for the control windings at junctions101 and 102 respectively.

Direction arrows are shown on the drawing to indicate the relativedirection of the flux generated by the several control windings.

In operation, under normal operating conditions the magnetic amplifier72 is biased to cut off. Assume, for purposes of illustration only, thatthe bias voltage at 102 is volts and the voltage at 101 is +20 volts.Further assume that the voltage drop across resistors 62 and 67 and thevoltage at terminal D is 20 volts. Also that the voltage at terminal Cis +20 volts. Under the above assumed conditions no current flows in thecontrol windings 81, 82, 83 and 84. Now assume the current flow in lines61, 64, 68 and 69 increase, the volt age drop across resistors 62, 67and 58 will increase. The voltage at A and B will be more negative orless positive than the bias voltage at junction 102, and a current willflow from junction 102 through blocking rectifiers 87 and 88 andwindings 82 and 83 to the negative terminals of rectifiers 55 and 56respectively. The voltage at C will be more positive than the voltage atjunction 101, therefore a current will flow from C through winding 81and rectifier 92 to junction 101. With a drop or loss of voltage at D,junction 102 will be less positive than D and current will flow from Dthrough winding '84 and rectifier 89 to junction 102. The currentflowing in the control windings will generate a flux sufiicient to buckout the bias flux and allow the magnetic amplifier to be turned on andoperate the relay 17.

Obviously many modifications and variations of the present invention arepossible in the light of the above teachings. It is therefore to beunderstood that within the scope of the appended claims the inventionmay be practiced otherwise than as specifically described.

What is claimed is:

1. In a protective system of the character described, relay means; aself-saturating magnetic amplifier comprising load windings and aplurality of control windings, said load windings having input circuitmeans and output circuit means; one of said control windings beingresponsive to an overcurrent condition, a second of said controlwindings being responsive to an overvoltage condition in said circuit tobe protected, a third of said control windings being responsive to anundervoltage of said circuit to be protected; circuit means connectingsaid output means to said relay means; and circuit means for connectingsaid input means to a voltage source; said magnetic amplifier beingresponsive to said plurality of control windings to control theoperation of said relay in response to overcurrent, overvoltage and/orundervoltage.

2. A system comprising; a transformer having a primary winding, first,second and third secondary winding, said primary winding being adaptedto be connected to a source of alternating current through a relay; afirst, second and third full wave rectifier connected across each ofsaid first, second and third secondary winding respectively; an outputsupply circuit connected to each of said full wave rectifiers; aresistor having a positive and negative terminal connected in serieswith each of said output supply circuits to provide a voltage dropproportional to the current flowing in the output supply circuit; amagnetic amplifier having input circuit means, output circuit means, anda bias winding; a source of reference potential having a positive and anegative terminal; a first control winding connected in series with ablocking rectifier between said negative terminal of one of said supplycircuit resistors and said negative terminal of said bias voltagesource, whereby a voltage drop across said resistor greater than thereference potential will cause a current to flow in said first controlwinding to permit saturation of said magnetic amplifier; a secondcontrol winding connected in series with a second rectifier between saidpositive terminal of another of said supply circuit resistors and saidpositive terminal of said reference source, whereby a voltage dropacross said other resistor greater than said reference potential willcause a current to flow in said second control winding to permitsaturation of said magnetic amplifier; a third control winding connectedin series with a third rectifier between the negative terminal of anegative supply circuit connected to the negative terminal of said thirdrectifier and the negative terminal of said bias source; the input ofsaid magnetic amplifier being connected to an alternating current sourceand the output of said magnetic amplifier being connected to said relay;whereby upon an overcurrent, overvoltage, and/ or undervoltage a fluxproduced by one of said control windings will oppose the bias fluxsufliciently to permit said magnetic amplifier to become saturated thuspermitting a current to flow in said load winding suflicient to actuatesaid relay.

References Cited in the file of this patent UNITED STATES PATENTS2,381,527 Traver Aug. 7, 1945 2,594,372 Wattenberger Apr. 29, 19522,677,800 Phillips May 4, 1954 2,709,774 Wells May 31, 1955 2,735,053Storey Feb. 14, 1956 2,735,060 Malick Feb. 14, 1956 2,757,320 Schuh July31, 1956 OTHER REFERENCES Magnetic Amplifiers (Eagan) Allis-ChalmersElectrical Review, Third Quarter 6, pages 20-29.

